Implantable stimulation devices are devices that generate and deliver electrical stimuli to body nerves and tissues for the therapy of various biological disorders, such as pacemakers to treat cardiac arrhythmia, defibrillators to treat cardiac fibrillation, cochlear stimulators to treat deafness, retinal stimulators to treat blindness, muscle stimulators to produce coordinated limb movement, spinal cord stimulators to treat chronic pain, cortical and deep brain stimulators to treat motor and psychological disorders, and other neural stimulators to treat urinary incontinence, sleep apnea, shoulder sublaxation, etc. The present invention may find applicability in all such applications, although the description that follows will generally focus on the use of the invention within a Spinal Cord Stimulation (SCS) system, such as that disclosed in U.S. Pat. No. 6,516,227, which is incorporated herein by reference in its entirety.
Spinal cord stimulation is a well-accepted clinical method for reducing pain in certain populations of patients. As shown in FIGS. 1A and 1B, a SCS system typically includes an Implantable Pulse Generator (IPG) 100, which includes a biocompatible case 30 formed of titanium for example. The case 30 typically holds the circuitry and power source or battery necessary for the IPG to function, although IPGs can also be powered via external RF energy and without a battery. The IPG 100 is coupled to electrodes 106 via one or more electrode leads (two such leads 102 and 104 are shown), such that the electrodes 106 form an electrode array 110. The electrodes 106 are carried on a flexible body 108, which also houses the individual signal wires 112 and 114 coupled to each electrode. The signal wires 112 and 114 are connected to the IPG 100 by way of an interface 115, which may be any suitable device that allows the leads 102 and 104 (or a lead extension, not shown) to be removably connected to the IPG 100. Interface 115 may comprise, for example, an electro-mechanical connector arrangement including lead connectors 38a and 38b configured to mate with corresponding connectors 119a and 119b on the leads 102 and 104. In the illustrated embodiment, there are eight electrodes on lead 102, labeled E1-E8, and eight electrodes on lead 104, labeled E9-E16, although the number of leads and electrodes is application specific and therefore can vary.
As shown in FIG. 2, the IPG 100 typically includes an electronic substrate assembly 14 including a printed circuit board (PCB) 16, along with various electronic components 20, such as microprocessors, integrated circuits, and capacitors mounted to the PCB 16. Two coils are generally present in the IPG 100: a telemetry coil 13 used to transmit/receive data to/from an external controller 12 as explained further below, and a charging coil 18 for charging or recharging the IPG's power source or battery 26 using an external charger (not shown). A feedthrough assembly 24 routes the various electrode signals from the electronic substrate assembly 14 to the lead connectors 38a, 38b, which are in turn coupled to the leads 102 and 104 (see FIGS. 1A and 1B). The IPG 100 further comprises a header connector 36, which among other things houses the lead connectors 38a, 38b. The IPG 100 can further include a telemetry antenna or coil 13 (discussed further below) for receipt and transmission of data to an external device such as a hand-held or clinician programmer (not shown), which can be mounted within the header connector 36. As already mentioned, the IPG 100 usually also includes a power source, and in particular a rechargeable battery 26.
Further details concerning the structure and function of typical IPGs and IPG systems are disclosed in U.S. patent application Ser. No. 11/305,898, filed Dec. 14, 2005, which is filed herewith via an information disclosure statement and which is incorporated herein by reference.
As one can appreciate, IPGs require programming data to function as required for a given patient. Typically, such programming data is wirelessly telemetered into the IPG 100 from the external controller 12. An exemplary external controller 12 is typically flat and fits in a patient's or clinician's hand for easy portable use in programming the IPG 100.
Wireless data telemetry between the IPG 100 and the external controller 12 is typically based on magnetic induction, and so requires telemetry coil 17 in the external controller 12 and telemetry coil 13 the IPG 100. When data is to be sent from the external controller 12 to the IPG 100, coil 17 is energized with alternating current (AC), which induces an electromagnetic field, which in turn induces a current in the IPG's telemetry coil 13. The power used to energize the coil 17 can come from a battery or batteries in the external controller (not shown), from a wall outlet via a plug (not shown), etc. The induced current can then be transformed at the IPG 100 back into the telemetered data signals. To improve the magnetic flux density, and hence the efficiency of the energy transfer, the IPG's telemetry coil 13 may be wrapped around a ferrite core 13′. As is well known, inductive transmission of data from coil 17 to coil 13 can occur transcutaneously, i.e., through the patient's tissue 25.
Optimally, IPG systems are simple enough that a patient or clinician can use the external controller 12 without medical supervision. This usually requires instruction on how to best use the external controller 12 in relation to the implanted IPG 100. Because the external controller 12 and IPG 100 are typically both flat, users are told that telemetry will be most efficient and effective when the distance between the external controller 12 and the IPG 100 is minimized; when the planes of these two devices are parallel; and when the devices “overlap” one another through the patient's tissue 25. Such instruction results from an understanding of the electromagnetic interaction of the coils 17 and 13, which is shown in FIG. 3. Shown is the optimal orientation of the two coils 17, 13 with respect to each other, with both coils lying in planes 50, 52 parallel to each other, and with the axis of both coils 54, 56 being colinear. When such an ideal condition is met, and assuming the distance D between the two coils is also minimized, energy transfer from coil 17 in the external controller 12 to coil 13 in the IPG 100 will be maximized.
However, realization of this ideal condition necessarily relies on successful implementation by the user of the external controller 12. For example, and as shown in FIG. 4, if the angle θ between the axis 54 of coil 17 and the axis 56 of coil 13 is non-ideal (i.e., non-zero), energy transfer will be non-ideal, which means that data may not be telemetered. When the axes 54, 56, are perpendicular, theoretically no energy will be transferred, and realistically only a negligible amount of energy will be transferred. Another non-ideal orientation between coil 17 and coil 13 is shown in FIG. 5. In this instance, the axes 54 and 56 of the coils are parallel, as are their planes 50 and 52, but they are not colinear, with the result that the coils are not overlapping. This too adversely impacts energy transfer from coil 17 to coil 13.
The non-ideal orientations depicted in FIGS. 4 and 5 illustrate that a user of an external controller 12 must be attentive to proper placement of the controller 12 relative to the IPG 100 and to the instructions noted earlier. Requiring correct implementation by the user is of course a drawback of such traditional IPG system hardware, because it is unrealistic to assume that any given user will be so attentive, and as a result data telemetry may be adversely affected.
Further exacerbating the potential problem of improper external controller-to-IPG orientation is the recognition that such an improper orientation is not necessarily always the result of user inadvertence. It has so far been assumed that it is relatively easy for the user to understand or infer the positioning of the coils 17 and 13. For example, when both the external controller 12 and the IPG 100 are basically flat, placing the coils 17, 13 close to the ideal orientation depicted in FIG. 3 is not difficult. But what if the external controller 12 or IPG 100 is not flat? What if the coils are mounted inside the housings in a manner in which the coil position cannot be inferred? What if the IPG 100 is implanted deep within a patient, such that the orientation of its coil 13 cannot be inferred through the patient's tissue? What if the IPG 100 moves or rotates within the patient after it is implanted? Any of these effects can make it difficult or impossible for even an attentive user to properly align the coil 17 in the external controller 12 and the coil 13 in the IPG 100.
An improved solution to this coil alignment problem would be one in which proper alignment between the external controller 12 and the IPG 100 could be reasonably assured, independent of their relative orientations. This disclosure provides embodiments of such a solution.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings.